Detergent compositions typically comprise one or more surfactants to provide cleaning. Such detergent compositions are often thickened to impart the desired rheology for their particular applications. A structurant may be used (either internal or external). This can impart higher levels of storage stability to the composition and it may provide it with enough structure to be able to suspend included solids or gasses, such as fragrance capsules or air bubbles.
Liquid detergent products present a challenge to formulators when it comes to structuring the compositions. One particular purpose of providing distinctive structure is to provide specific flow behavior. Specific types of applications often require specific flow behavior. Another common purpose of providing structure is to enable suspending solid particles in the detergent matrix, or dispersing liquids which are immiscible in the detergent matrix. In non-structured liquid detergent or personal care products, the presence of such ingredients generally leads to sedimentation or phase separation and therefore renders such detergents unacceptable from a consumer's viewpoint.
Hence, two structuring properties are typically desired in liquid detergent and personal care products: shear thinning capabilities and bead and/or particle suspension capabilities. The capability to suspend particles in principle is characterized by the yield stress value. High zero-shear viscosity values may also be indicative of particle suspension capability. Shear thinning capabilities are typically characterized by the pouring viscosity and the ratio of the pouring viscosity and low-stress viscosity values. As will be understood, the ability of a certain structuring agent to provide shear thinning capabilities alone is insufficient to determine whether the liquid product is capable of suspending bead particles with sufficient stability and vice versa. Structuring benefits are desired at as low a level of external structurant as possible for cost and formulation concerns. For example, excessive amounts of external structuring agent may provide the particle suspension capability but result in the liquid composition becoming overly viscous and non-pourable.
It is also relevant that a structuring agent can be applied in highly concentrated liquid detergent compositions, which have low dosage volumes with high cleaning performance. Many attempts have been and still are made to produce concentrated products containing less than 50% water and high active ingredient levels. These low dosage concentrated products are in high demand since they conserve resources and can be sold in small packages. The stabilization of liquid detergent products containing very high levels of surfactants and other active ingredients and lower levels of water has proven to be particularly challenging. A further relevant trend seen in the field of liquid detergent products is the increasing demand for bio-based products, to reduce the environmental impact of the products.
Conventional approaches for providing distinctive structure to liquid detergent and personal care products include the addition of specific structuring agents, including both internal and external structuring agents. Examples of known internal structuring agents include: surfactants and electrolytes. External structuring agents include polymers or gums, many of which are known to swell or expand when hydrated to form random dispersion of independent microgel particles. Examples include acrylate polymers, structuring gums (e.g., xanthan gum), starch, agar, hydroxyl alkyl cellulose etc. Although gums have been used to provide structuring benefits, the gums are pH dependent, i.e., failing at pH above 10. The stability of gums is also unsatisfactory at high electrolyte concentrations. Further, certain gums have been found to be susceptible to degradation in the presence of detersive enzymes. Thus, there remains a need for other external structuring agents less susceptible to these and other known problems. When large particles are suspended (e.g., polyethylene particles, guar beads), levels of polymer used is typically 1% or more.
It has previously been shown that when certain fibrous polymers (e.g., micro fibrous cellulose with large aspect ratios) are used as structurants, these may provide efficient suspending properties (see e.g. U.S. Pat. No. 7,776,807, US2008/0108541, US2008/0146485, and WO2013/160023). The fibrous polymers are believed to form spider network like structures which efficiently trap the particles inside the network and thereby impart good suspending properties. The polymers are said to provide excellent rheological properties and are said to be salt tolerant if salt is used in the formulation. Another material reported to provide structuring benefits is bacterial cellulose. Bacterial cellulose is typically cultured using a bacterial strain of Acetobacter aceti var. xylinum and dried using spray drying or freeze drying techniques. Attempts to manufacture and prepare the dried bacterial cellulose compositions which can be rehydrated and activated into a particulate cellulose material for use in end products are known.
WO 2014/017913 discloses a liquid detergent composition comprising an external structuring agent, which are parenchymal cellulose based materials, comprising cell wall material and their networks of cellulose based fibers and nanofibrils. WO 2014/142651 discloses that the parenchymal cellulose based materials can advantageously be used for stabilization of suspended solid particles or gas bubbles in the liquid detergent compositions and fragrance compositions. Each of these documents is incorporated by reference in their entireties herein.
The inventors surprisingly discovered that the use of a clay as a co-structuring agent enhances the stability of an aqueous detergent composition containing the external structuring agent. The use of a composition containing both the external structuring agent and a clay results in a more stable aqueous detergent composition having shear thinning capabilities and sufficient stability and particle suspension capabilities while avoiding one or more of the above mentioned problems encountered with prior art formulations.